In efforts to reduce the overall weight of gas turbine engines, lighter-weight materials have been implemented for many different components within the engine. For example, gas turbine engine fan blades have been manufactured from titanium, but in more recent designs, fan blades are manufactured from aluminum or composite materials. The aluminum or composite fan blades do not share the same impact strength properties of titanium fan blades. As such, the aluminum or composite fan blades are typically equipped with a protective sheath along their leading edge to improve impact strength and prevent blade damage from foreign object impact, such as impact with birds, hail or other debris, which may lead to catastrophic engine failure or secondary damage downstream of the fan blades. Often times the sheaths are made from titanium or other high strength materials protecting the aluminum or composite fan blades from blade damage such as cracking, delamination, deformation or erosion caused by impacting foreign objects.
Certain portions of the fan blade experience significantly more stress and strain than other portions during foreign object impact. One such portion is the leading edge area adjacent the root of the fan blade. This area is particularly vulnerable during impact because a relatively significant decrease in area thickness begins where the blade transitions to the root region. Increasing the thickness in this area of the fan blade provides a desired strengthening for a more structural blade. This increase will necessarily increase the sheath area for this portion of the fan blade as well. However, because the sheath is in the flowpath, it is desirable to maintain a minimum amount of sheath material along the rest of the fan blade while increasing the amount of sheath material corresponding to the increased area of the fan blade.
Accordingly, there is a need to provide a sheath that accommodates an increased structural thickness of a fan blade area, where the blade transitions to the root region, while maintaining a minimum amount of sheath material that covers the fan blade along the other area of the leading edge.